1) Field of the invention
The invention relates to transmission devices for converting vehicles with a front cab, to front-wheel drive, vehicles with a chassis to which bodywork may be added. The invention relates more particularly to vehicles intended, from the outset or after conversion, to take a lowered platform, especially showman's vehicles, mobile laboratories, or travelling sales vehicles.
2) Description of the prior art
For obvious reasons of cost reduction, the manufacturers of vehicles for specific uses like those described hereinabove generally make use of standard vehicle chassis supplied by the large manufacturers or by specialized manufacturers.
The case of vehicles with a lowered rear platform poses a problem in this respect.
This is because the lowered platform forces the manufacturer to use basic vehicles with front-wheel drive; this does not pose great problems for vehicles of limited power (van type) which offer a huge choice in this range of vehicle.
However, if a heavier vehicle (over 6 tonnes) is desired, the commonest basic vehicles are haulage vehicles with a front cab originally designed for propulsion, (i.e. rear wheel drive) or even for all-wheel drive, or which include a transmission system derived from 4.times.4 or 6.times.6 drive as described e.g. in U.S. Pat. No. 3,656,573. As a consequence, the drive system gearbox+transmission! on these basic vehicles occupies a substantial length starting behind the cab, and this correspondingly limits the possible length of the lowered platform. Such a transmission system additionally leads to not insignificant mechanical losses due to friction.